Mechanical key actuated locks, even the highest security types such as axial pin tumbler locks, are oftentimes defeated by picking. In the ancient art of locks, it is an accepted fact that there is a continual counteraction between designing more pick resistent devices and the devising of ways of opening such locks without the proper key. Thus, lock manufacturers have come to accept as a fundamental fact that no lock can absolutely prevent intrusion but depending upon the economics and degree of security required, lock designers concentrate upon two basic lock functions which are to make the potential intruder expend time and make noise.
There are innumerable mechanical refinements which have been proposed and undoubtedly will continue to come about that are directed to increasing the amount of skill and therefore the time required to pick or defeat the lock. For example, in one of my prior axial pin tumbler lock patents, U.S. Pat. No. 3,903,720, a cam plate arrangement is disclosed which has an array of openings corresponding with locking pin stems which will hinder the application of the required torque making the lock less susceptable to easy picking especially with certain available tools that have been devised to simulate a key. This with other features of the lock increase the time factor by thwarting simultaneous multiple pin manipulation instead of one pin at a time manipulation.
To provide the function of noise, approaches such as disclosed in U.S. Pat. Nos. 3,878,700; 3,986,376 and 4,078,405, among others, have come about where a pin stem functions as an electrical contact to complete a circuit and actuate an alarm if there is an unauthorized tampering with the lock.
With any of such arrangements, the contact element itself provides not only a physical feel of a limit of pin movement, but it also gives the tamperer an audible reference from which to locate the shear plane. In order to circumvent this infirmity such prior patentees contemplated electrical circuitry which would lock in the alarm once any contact is made and the alarm would continue to sound until it is shut off by authorized personnel having a proper key who can gain access to a reset switch or the like.
Since the use of this type of lock with alarm triggering capability is desirable for vending machines which oftentimes are in locations where continuous and long term sounding of an alarm would be an excessive disturbance to others such as hotel or motel guests, latching in circuits even with timed shutoffs may not be acceptable.
Accordingly, it is a primary object of the invention to provide an axial pin tumbler lock with alarm triggering capabilities which also resists simple picking efforts thereby increasing the manipulation time required in any attempted picking. In this connection, it is a related object to provide an improved axial pin tumbler lock with alarm triggering capability of the aforementioned type which will more closely associate the alarm sounding with tampering actions requiring a greater time span for manipulations that is more apt to discourage or drive away a prospective tamperer.
Another object is to provide such an axial pin tumbler lock with alarm triggering capability that can be conveniently provided in the most conventional and widely used size for axial pin tumbler locks.